WOODS OF THE VITACEAE - FOSSIL AND MODERN

Vitaceoxylon tiffneyi gen. et sp. nov. and Vitaceoxylon carlquistii sp . nov. from the Middle Eocene Clarno formation are the oldest known wo ods with characteristics of the Vitaceae. They are characterized by a tendency to two diameter classes of vessels, wide and tall rays, and a high proportion of their area is vessel. Other characteristics includ e septate imperforate elements, scanty paratracheal to vasicentric par enchyma, idioblasts in the rays, crowded alternate intervessel pitting , and vessel-parenchyma pits with reduced borders. Wood anatomy of the major extant genera of Vitaceae was examined and compared to the foss ils. Features of secondary xylem useful for distinguishing between gen era in the Vitaceae include vessel size and arrangement (two distinct diameter classes or not, radial multiples or tendency to tangential mu ltiples), vessel pitting (scalariform or alternate), crystal type (pri smatic, druses, and/or raphides) and location (in chambered parenchyma and/or ray parenchyma), cambial variants (present or absent). Wood an atomy supports the proposed close relationship of Cissus to Cayratia. Pronounced vessel dimorphism occurs in temperate Vitaceae; cambial var iant structure occurs in tropical Vitaceae. Despite their conformity w ith Vitaceae at the family level, the two fossil woods are not compara ble to any one extant genus. This contrasts with the Vitaceae seeds fr om Clarno, all of which are referable to extant genera. Two new combin ations for fossil woods of the Vitaceae are proposed: Vitaceoxylon amp elopsoides (Schonfeld) comb. nov., and Vitaceoxylon megyazoense (Gregu ss) comb. nov.